As someone who recently interviewed (although not at Facebook) the number is the _annual compensation package at the time they signed their offer_ (it includes base salary + annual stock grant + bonus). If someone got $1,000,000 in annual compensation 2 years ago, the stock portion per year will likely be larger now due to appreciation of the stock. These numbers are crazy high and before I interviewed this time around I was somewhat skeptic of how real these numbers were outside of a few outliers but now I'm pretty sure it's pretty common.